The galvanic connection of electrical signals in so-called crossbar switches is already known. For example, there is illustrated in the French design making 2.447.623 a galvanic crossbar switch with a plurality of incoming conductors in one plane (x) and a plurality of outgoing conductors in another plane (y). The conductors in the x plane and the y plane form a matrix with a plurality of cross points. These cross points can be connected together by activating switching rods at each cross point.
Particularly with access networks in the art of telephony there is a need of automatic, remotely controlled crossbar switches for avoiding sending out personnel for connecting cable pairs in buldings and distribution cabinets. On the station side there is the same problem in switching between different types of service units and in broken-out units for connecting telephone subscribers such as broken-out subscriber stages and line circuits. For these applications galvanic switching is the most suitable method of operation.
Crossbar switches of the kind mentioned above are also desired for enabling measurements on lines, by connecting the measuring equipment galvanically to the line. These crossbar switches must have great reliability, must not malfunction if there is a power failure and must not take any power in an inoperative state. The demands made according to the above on this equipment makes it unsuitable to introduce electronics in the parts which are to provide the connection paths between incoming and departing conductors.
The crossbar switch according to the above mentioned French design patent can indeed be used for the purposes mentioned above, but is limited to making or opening individual, separate cross points in the matrix, and can be only used for low frequencies.